1. Field of the Invention
The present invention relates to a device for processing and interpreting drilling data, which is placed at the bottom of a well and, more particularly, to such a device intended to be used in oil drilling.
The present invention also relates to a method enabling this device to be implemented.
2. Description of Related Art
During the drilling of a well, for example an oil well, it is desirable for the foreman driller to ascertain the behaviour of the assembly and of the tool at the bottom of the well so as to monitor the drilling parameters better. It is preferable to ascertain these conditions in real time, this necessitating means for transmitting data from the bottom of the well to the surface.
Ascertaining the downhole conditions makes it possible to drill more assuredly and to reduce the drilling costs. Moreover, the foreman driller will have the option of reacting quickly to any downhole event, for example, change of rock type, wear of the tool or mechanical instability.
Several means for transmitting data from the bottom to the surface have been proposed. Among these means is transmission by electrical conductor, or by electromagnetic waves. Data transmission by pressure waves in the drilling mud has also been proposed. In such a system, the pressure of the mud circulating around the drill string is modulated for example by way of a servo valve mounted in a sub-unit placed in the drill string adjacent to the tool.
The pressure waves propagate at around 1500 m/s; they undergo numerous reflections between bottom and surface.
In view of the deterioration in the limitations inherent in modulating the pressure of the mud, and the need to preserve the quality of the data, the data flow rate remains low.
Currently, the data transmission flow rate does not exceed a few bits per second.
In the future, whatever the improvements in the systems for transmitting data in the mud, the speed of transmitting data from the bottom to the surface will remain limited.
In order to alleviate this disadvantage, the data should be preprocessed at the bottom, thus very significantly reducing the volume of the signals to be transmitted to the surface.
Document GB-A-2,216.661 describes a device for measuring the vibrations of a drill string, placed at the bottom of the well, and which includes a processor intended to record the data provided by an accelerometer. The device detects the acceleration levels which exceed a predetermined value and these levels alone are signalled to the surface. Hence, in this device, data which depend on a single parameter are sent to the surface only when a predetermined threshold is crossed, and this without any analysis of physical behaviour having been undertaken.